Abstract: A processor of a computer-aided design system reads and executes a software stored in a memory to input first digital data of a first component of the composite object, input second digital data of a second component of the composite object, analyze the first digital data and the second digital data with first criterion to obtain a plurality of first surfaces and a plurality of second surfaces respectively, calculate a distance between one of the plurality of the first surfaces and one of the plurality of the second surfaces, and output a first result when the distance is greater than or equal to the first threshold; otherwise, output a second result.